As a circuit scheme for a gas-insulated switchgear, a bus scheme with a so-called 1½ CB (Circuit Breaker) structure may be adopted when high reliability is required at a large-capacity electric power substation or the like. The gas-insulated switchgear of this bus scheme has three circuit breakers forming a unit structure connected in series and disposed between main buses in a pair. That is, in this scheme, for the purpose of leading two circuits, three circuit breakers are used, thereby preventing the system from being affected even in the case of a bus trouble. Also, consideration is given such that checking the circuit breakers and others does not involve a suspension of lines.
As a conventional technology adopting a bus scheme of this 1½ CB structure, for example, there is a gas-insulated switchgear disclosed in a first patent document. In the first patent document, first, second, and third circuit breakers each having disconnect switches attached on both sides are electrically connected in series, and the first and third circuit breakers each have its one end connected to a main bus. Also, branch buses are drawn from a portion between the first circuit breaker and the second circuit breaker and a portion between the second circuit breaker and the third circuit breaker. Furthermore, a two-directional branch is provided to either one of the disconnect switches attached to the first, second, and third circuit breakers and facing each other, and its branching portion has a branch bus connected thereto.
First patent document: Japanese Patent Application Laid-open No. 2002-186124 (p. 2, FIG. 1)